1. Field of the Invention
The present invention relates to a chassis frame formed by joining an end portion of a joining member in abutting contact with an outer face of a joined member, e.g., an octothorp-shaped chassis frame formed by joining an end portion of a side member in abutting contact with an outer face of an end cross member or by joining an end portion of a cross member in abutting contact with an outer face of a side member.
The “side members” defined in the present invention are a pair of symmetrical structural members extending in a direction of forward and backward movements of a vehicle. The “end cross member” is a structural member installed at a pair of joints formed at an each end portion of the side members in an orthogonal direction to the direction of forward and backward movements of the vehicle to form a front edge or a rear edge of the chassis frame, and it is exemplified as either a front end cross member or a rear end cross member. The “cross member” is a structural member installed between the side members in the orthogonal direction to the direction of forward and backward movements of the vehicle.
2. Description of the Related Art
A chassis frame which is a mount for an engine of an automobile or the like is formed into an octothorp shape by joining joints formed at an each end portion of side members in abutting contact with an outer face of a front end cross member or a rear end cross member, or by joining opposite ends of the cross member in abutting contact with outer faces of the side members, for example. In this chassis frame, not only rigidity of each member as a component but also joining strength and rigidity of each joined part between the respective members need to be enhanced. In order to enhance the joining strength and the rigidity of each joined part between the respective members, various techniques have been conventionally proposed.
There is a conventional art disclosed in Japanese Patent Application Laid-open No. 10-338161 in which “a brace of a half-cut horn shape” is attached to an end of a cross member particularly as a joined part to the cross member bridged between side members. It describes that rigidity of the frame can be enhanced by welding a bracket to the end of the cross member.
There is another conventional art disclosed in Japanese Patent Application Laid-open No. 2000-203452 in which the joined parts are individually formed by placing a bracket to a joint formed at each end portion of a side member bifurcated at a front end thereof. In the joined parts in this Japanese Patent Application Laid-open No. 2000-203452, the bracket has a function of accommodating the height difference caused by an uneven cross member and to thereby align a central axis of the cross member with a central axis of the side member.
Japanese Patent Application Laid-open No. 2002-120754 designs to enhance rigidity of a joined part. At the joined part of this conventional art, a flange is formed at each end portion of a cross member formed by combining and joining two members having angular U cross-sectional shapes, and a side member is arc-welded to the flange. The side member is not provided with a hole for attaching a cross member. Cross member reinforcements are attached respectively from right and left sides so as to sandwich the joined part between both the side member and the cross member, and the cross member reinforcements and both the members are joined by all around arc-welding. In this way, not only rigidity of the joined part but also flexural rigidity and torsional rigidity of the whole chassis frame are enhanced.
A case in which a joint formed at an end portion of a side member is joined in abutting contact with an outer face of a front end cross member will be described below as an example.
In each of the above-described conventional arts, an additional auxiliary member is attached to a joint formed at an end portion of a side member to enhance joining strength and rigidity of the joined part. It is true that the joining strength or rigidity is enhanced by attaching the auxiliary member, but increase in number of members results in increase in number of process steps and cost of manufacturing.
Therefore, a joined part formed without using such auxiliary member is also frequently used. Such a joined part is formed by cutting a joint at an end portion of a side member with a laser or the like so that the joint has a shape following a pattern of an outer face of a front end cross member and bringing this joint into close contact with the outer face of the front end cross member. However, such cutting process of the joint formed at the end portion of the side member increases machining cost due to use of the laser and to secure high dimensional accuracy. Moreover, to weld a joint between members intersecting with each other at acute angles is of poor durability.
In view of above, therefore, the inventors of the present invention have studied to develop a chassis frame including a joined part which can be formed without using an auxiliary member so as to reduce number of members and without cutting process by using a laser while achieving high joining strength and rigidity.